Waste Water Reuse

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3.2 Wastewater reuse

Once freshwater has been used for an economic or beneficial purpose, it is generallydiscarded as waste. In many countries, these wastewaters are discharged, either asuntreated waste or as treated effluent, into natural watercourses, from which they areabstracted for further use after undergoing "self-purification" within the stream. Throughthis system of indirect reuse, wastewater may be reused up to a dozen times or morebefore being discharged to the sea. Such indirect reuse is common in the larger riversystems of Latin America. However, more direct reuse is also possible: the technologyto reclaim wastewaters as potable or process waters is a technically feasible option foragricultural and some industrial purposes (such as for cooling water or sanitaryflushing), and a largely experimental option for the supply of domestic water.Wastewater reuse for drinking raises public health, and possibly religious, concerns

among consumers. The adoption of wastewater treatment and subsequent reuse as ameans of supplying freshwater is also determined by economic factors.

In many countries, water quality standards have been developed governing thedischarge of wastewater into the environment. Wastewater, in this context, includessewage effluent, stormwater runoff, and industrial discharges. The necessity to protectthe natural environment from wastewater-related pollution has led to much improvedtreatment techniques. Extending these technologies to the treatment of wastewaters topotable standards was a logical extension of this protection and augmentation process.

Technical Description

One of the most critical steps in any reuse program is to protect the public health,especially that of workers and consumers. To this end, it is most important to neutralizeor eliminate any infectious agents or pathogenic organisms that may be present in thewastewater. For some reuse applications, such as irrigation of non-food crop plants,secondary treatment may be acceptable. For other applications, further disinfection, bysuch methods as chlorination or ozonation, may be necessary. Table 18 presents arange of typical survival times for potential pathogens in water and other media.

Table 18 Typical Pathogen Survival Times at 20 - 30C (in days)

PathogenFreshwater and sewage Crops SoilViruses < 120 but usually


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A typical example of wastewater reuse is the system at the Sam Lords Castle Hotel inBarbados. Effluent consisting of kitchen, laundry, and domestic sewage ("gray water") iscollected in a sump, from which it is pumped, through a comminutor, to an aerationchamber. No primary sedimentation is provided in this system, although it is oftendesirable to do so. The aerated mixed liquor flows out of the aeration chamber to a

clarifier for gravity separation. The effluent from the clarifier is then passed through a16-foot-deep chlorine disinfection chamber before it is pumped to an automatic sprinklerirrigation system. The irrigated areas are divided into sixteen zones; each zone hastwelve sprinklers. Some areas are also provided with a drip irrigation system. Sludgefrom the clarifier is pumped, without thickening, as a slurry to suckwells, where it isdisposed of. Previously the sludge was pumped out and sent to the Bridgetown SewageTreatment Plant for further treatment and additional desludging.

Extent of Use

For health and aesthetic reasons, reuse of treated sewage effluent is presently limited

to non-potable applications such as irrigation of non-food crops and provision ofindustrial cooling water. There are no known direct reuse schemes using treatedwastewater from sewerage systems for drinking. Indeed, the only known systems of thistype are experimental in nature, although in some cases treated wastewater is reusedindirectly, as a source of aquifer recharge. Table 19 presents some guidelines for theutilization of wastewater, indicating the type of treatment required, resultant waterquality specifications, and appropriate setback distances. In general, wastewater reuseis a technology that has had limited use, primarily in small-scale projects in the region,owing to concerns about potential public health hazards.

Wastewater reuse in the Caribbean is primarily in the form of irrigation water. In

Jamaica, some hotels have used wastewater treatment effluent for golf course irrigation,while the major industrial water users, the bauxite/alumina companies, engage inextensive recycling of their process waters (see case study in Part C, Chapter 5). InBarbados, effluent from an extended aeration sewage treatment plant is used for lawnirrigation (see case study in Part C, Chapter 5). Similar use of wastewater occurs onCuraao.

Table 19 Guidelines for Water Reuse

Type of ReuseTreatmentRequired

ReclaimedWater

Quality

RecommendedMonitoring

SetbackDistances

AGRICULTURAL SecondaryDisinfection

pH = 6-9 pH weekly 300 ft frompotable watersupply wells

Food cropscommerciallyprocessed

BOD e 30mg/l

BOD weekly

SS = 30 mg/l SS daily

Orchards and FC e 200/100 FC daily 100 ft from


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Vinerds ml areasaccessible to

publicCl2 residual =1 mg/l min.

Cl2 residualcontinuous

PASTURAGE SecondaryDisinfection

pH = 6-9 pH weekly 300 ft frompotable watersupply wellsPasture for milkinganimals

BOD e 30mg/l

BOD weekly

SS e 30 mg/l SS daily

Pasture for livestock FC e 200/100ml

FC daily 100 ft fromareas

accessible topublic

Cl2 residual =1 mg/l min.


FORESTATION SecondaryDisinfection


BOD e 30

mg/l

BOD weekly

SS e 30 mg/l SS daily

FC e 200/100ml

FC daily 100 ft fromareas

accessible tothe public



AGRICULTURAL SecondaryFiltrationDisinfection


Food crops notcommerciallyprocessed

BOD e 30mg/l

BOD weekly

Turbidity e 1NTU

Turbidity daily

FC = 0/100 ml FC daily



GROUNDWATERRECHARGE

Site-specificand use-dependent

Site-specificand use-

dependent

Depends ontreatment and use

Site-specific

Source: USEPA, Process Design Manual: Guidelines for Water Reuse, Cincinnati, Ohio,1992, (Report No. EPA-625/R-92-004).In Latin America, treated wastewater is used in small-scale agricultural projects and,particularly by hotels, for lawn irrigation. In Chile, up to 220 l/s of wastewater is used forirrigation purposes in the desert region of Antofagasta. In Brazil, wastewater has beenextensively reused for agriculture. Treated wastewaters have also been used for humanconsumption after proper disinfection, for industrial processes as a source of coolingwater, and for aquaculture. Wastewater reuse for aquacultural and agricultural irrigationpurposes is also practiced in Lima, Peru. In Argentina, natural systems are used for


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wastewater treatment. In such cases, there is an economic incentive for reusingwastewater for reforestation, agricultural, pasturage, and water conservation purposes,where sufficient land is available to do so. Perhaps the most extensive reuse ofwastewater occurs in Mexico, where there is large-scale use of raw sewage for theirrigation of parks and the creation of recreational lakes.

In the United States, the use of reclaimed water for irrigation of food crops is prohibitedin some states, while others allow it only if the crop is to be processed and not eatenraw. Some states may hold, for example, that if a food crop is irrigated in such a waythat there is no contact between the edible portion and the reclaimed water, adisinfected, secondary-treated effluent is acceptable. For crops that are eaten raw andnot commercially processed, wastewater reuse is more restricted and less economicallyattractive. Less stringent requirements are set for irrigation of non-food crops.

International water quality guidelines for wastewater reuse have been issued by theWorld Health Organization (WHO). Guidelines should also be established at national

level and at the local/project level, taking into account the international guidelines. Somenational standards that have been developed are more stringent than the WHOguidelines. In general, however, wastewater reuse regulations should be strict enoughto permit irrigation use without undue health risks, but not so strict as to prevent its use.When using treated wastewater for irrigation, for example, regulations should be writtenso that attention is paid to the interaction between the effluent, the soil, and thetopography of the receiving area, particularly if there are aquifers nearby.

Operation and Maintenance

The operation and maintenance required in the implementation of this technology is

related to the previously discussed operation and maintenance of the wastewatertreatment processes, and to the chlorination and disinfection technologies used toensure that pathogenic organisms will not present a health hazard to humans.

Additional maintenance includes the periodic cleaning of the water distribution systemconveying the effluent from the treatment plant to the area of reuse; periodic cleaning ofpipes, pumps, and filters to avoid the deposition of solids that can reduce thedistribution efficiency; and inspection of pipes to avoid clogging throughout thecollection, treatment, and distribution system, which can be a potential problem. Further,it must be emphasized that, in order for a water reuse program to be successful,stringent regulations, monitoring, and control of water quality must be exercised in orderto protect both workers and the consumers.

Level of Involvement

The private sector, particularly the hotel industry and the agricultural sector, arebecoming involved in wastewater treatment and reuse. However, to ensure the publichealth and protect the environment, governments need to exercise oversight of projectsin order to minimize the deleterious impacts of wastewater discharges. One element ofthis oversight should include the sharing of information on the effectiveness of


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wastewater reuse. Government oversight also includes licensing and monitoring theperformance of the wastewater treatment plants to ensure that the effluent does notcreate environmental or health problems.

Costs

Cost data for this technology are very limited. Most of the data relate to the cost oftreating the wastewater prior to reuse. Additional costs are associated with theconstruction of a dual or parallel distribution system. In many cases, these costs can berecovered out of the savings derived from the reduced use of potable freshwater (i.e.,from not having to treat raw water to potable standards when the intended use does notrequire such extensive treatment). The feasibility of wastewater reuse ultimatelydepends on the cost of recycled or reclaimed water relative to alternative supplies ofpotable water, and on public acceptance of the reclaimed water. Costs of effluenttreatment vary widely according to location and level of treatment (see the previoussection on wastewater treatment technologies). The degree of public acceptance also

varies widely depending on water availability, religious and cultural beliefs, and previousexperience with the reuse of wastewaters.

Effectiveness of the Technology

The effectiveness of the technology, while difficult to quantify, is seen in terms of thediminished demand for potable-quality freshwater and, in the Caribbean islands, in thediminished degree of degradation of water quality in the near-shore coastal marineenvironment, the area where untreated and unreclaimed wastewaters were previouslydisposed. The analysis of beach waters in Jamaica indicates that the water quality isbetter near the hotels with wastewater reuse projects than in beach areas where reuse

is not practiced: Beach #1 in Table 20 is near a hotel with a wastewater reuse project,while Beach #2 is not. From an aesthetic point of view, also, the presence of lushvegetation in the areas where lawns and plants are irrigated with reclaimed wastewateris further evidence of the effectiveness of this technology.

Table 20 Water Quality of Beach Water in Wastewater Reuse Project in Jamaica

Site BOD TC FC NO3Beach #1 0.30


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there is a water deficit for several months of the year, implementation of wastewaterrecycling or reuse by industries can reduce demands for water of potable quality, andalso reduce impacts on the environment.

Large-scale wastewater reuse can only be contemplated in areas where there are

reticulated sewerage and/or stormwater systems. (Micro-scale wastewater reuse at thehousehold or farmstead level is a traditional practice in many agricultural communitiesthat use night soils and manures as fertilizers.) Urban areas generally have seweragesystems, and, while not all have stormwater systems, those that do are ideal localitiesfor wastewater reuse schemes. Wastewater for reuse must be adequately treated,biologically and chemically, to ensure the public health and environmental safety. Theprimary concerns associated with the use of sewage effluents in reuse schemes are thepresence of pathogenic bacteria and viruses, parasite eggs, worms, and helminths (allbiological concerns) and of nitrates, phosphates, salts, and toxic chemicals, includingheavy metals (all chemical concerns) in the water destined for reuse.

Advantages

y This technology reduces the demands on potable sources of freshwater.

y It may reduce the need for large wastewater treatment systems, if significant portionsof the waste stream are reused or recycled.

y The technology may diminish the volume of wastewater discharged, resulting in abeneficial impact on the aquatic environment.

y Capital costs are low to medium, for most systems, and are recoverable in a very

short time; this excludes systems designed for direct reuse of sewage water.

y Operation and maintenance are relatively simple except in direct reuse systems,where more extensive technology and quality control are required.

y Provision of nutrient-rich wastewaters can increase agricultural production in water-poor areas.

y Pollution of seawater, rivers, and groundwaters may be reduced.

y Lawn maintenance and golf course irrigation is facilitated in resort areas.

y In most cases, the quality of the wastewater, as an irrigation water supply, is superiorto that of well water.Disadvantages


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y If implemented on a large scale, revenues to water supply and wastewater utilitiesmay fall as the demand for potable water for non-potable uses and the discharge ofwastewaters is reduced.

y Reuse of wastewater may be seasonal in nature, resulting in the overloading of

treatment and disposal facilities during the rainy season; if the wet season is of longduration and/or high intensity, the seasonal discharge of raw wastewaters may occur.

y Health problems, such as water-borne diseases and skin irritations, may occur inpeople coming into direct contact with reused wastewater.

y Gases, such as sulfuric acid, produced during the treatment process can result inchronic health problems.

y In some cases, reuse of wastewater is not economically feasible because of therequirement for an additional distribution system.

y Application of untreated wastewater as irrigation water or as injected recharge watermay result in groundwater contamination.Cultural Acceptability

A large percentage of domestic water users are afraid to use this technology to supplyof potable water (direct reuse) because of the potential presence of pathogenicorganisms. However, most people are willing to accept reused wastewater for golfcourse and lawn irrigation and for cooling purposes in industrial processes. On thehousehold scale, reuse of wastewaters and manures as fertilizer is a traditional

technology.

Further Development of the Technology

Expansion of this technology to large-scale applications should be encouraged. Citiesand towns that now use mechanical treatment plants that are difficult to operate,expensive to maintain, and require a high skill level can replace these plants with thesimpler systems; treated wastewater can be reused to irrigate crops, pastures, andlawns. In new buildings, plumbing fixtures can be designed to reuse wastewater, as inthe case of using gray water from washing machines and kitchen sinks to flush toiletsand irrigate lawns. Improved public education to ensure awareness of the technology

and its benefits, both environmental and economic, is recommended.

Information Sources

Contacts


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Carlos Sols Morelos, Centro Interamericano de Recursos de Agua de la UniversidadAutnoma del Estado de Mxico (UAEM), Facultad de Ingeniera, Cdigo Postal 50110, Cerro de Coatepec, Toluca, Mxico. Tel. (52-72)20-1582. Fax (52-72)14-4512.

Basil P. Fernandez, Managing Director, Water Resources Authority, Hope Gardens,

Post Office Box 91, Kingston 7, Jamaica. Tel. (809)927-1878. Fax (809)977-0179.

Armando Llop and GracielaFasciolo, Instituto Nacional de Ciencia y Tcnica Hdrica(INCYTH/CELAA), Belgrano 210 Oeste, 5500 Mendoza, Argentina. Tel. (54-61)28-7921. Fax (54-91)28-5416.

GuillermoNavas Brule, Codelco Chile, Div. Chuquicamata, Calama, Chile. Tel. (56-56)32-2207. Fax (56-56)32-2207.

Alberto Cceres Valencia, Gerente de Ingenieria, Empresa de Servicios Sanitarios deAntofagasta S.A., Manuel Verbal 1545, Santiago, Chile. Tel. (56-55)26-7979. Fax (56-

55)22-4547.

Vincent Sweeney, Caribbean Environment Health Institute (CEHI), Post Office Box1111, Castries, St. Lucia. Tel. (809)452-2501. Fax (809)453-2721. E-mail:[email protected].

Ernesto Prez, P.E., Technology Transfer Chief, Water Management Division, USEPARegion IV, 345 Courtland Street N.E, Atlanta, Georgia 30365, U.S.A.. Tel. (404) 347-3633.

OscarVlez, Ingeniero Sanitario Subinterventor, OSM - SE, Belgrano 920, 5500

Mendoza, Argentina. Tel. (54-61)25-9326. Fax (54-61)25-9326.

Pedro Mancuso, Faculdade de Sade Pblica da Universidade de So Paulo,Departamento de Sade Ambiental, 01255-090 So Paulo, So Paulo, Brasil. Tel. (55-11)872-3464. Fax (55-11)853-0681.

Bibliography

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Barbosa, M., and G. Sarmiento. 1988. Estudios de Tratabilidad de las AguasResiduales de Bogot, Colector Salitre. Bogot, Empresa de Acueducto y Alcantarilladode Bogot, LAN-10. (Discos Biolgicos Rotatorios)

Cornejo, E., and R. Berolatti. 1991. Tratamiento de Aguas Servidas Mediante el Uso deMacrfitos Acuticos. Puno, Peru, Convnio UNA-UBC-ACDI, IIAA.


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Fair, G. 1989. Purificacin de Aguas y Tratamiento de Aguas Servidas. vol II. Mexico,D.F., Limusa. Guyot, J. P. 1988. Microbiologa de la Digestin Anaerbica. Medelln,Colombia, Universidad de Antioqua.

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Lettinga, G., et al. 1989. "High Rate Anaerobic Waste Water Treatment Using the UASBReactor Under a Wide Range of Temperature Conditions," Biotechnology and GeneticEngineering Review, 2.

Martnez, I. 1989. Depuracin de Aguas con Plantas Emergentes. Madrid, Ministrio deAgricultura, Pesca y Alimentacin.

Reed, S.C., E.J. Middlebrooks, and R.W. Crites. 1988. Natural Systems for WasteManagement and Treatment. New York, McGraw-Hill.

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----. 1980. Planning Wastewater ManagementFacilities for Small Communities.Cincinnati, Ohio. (Report No. EPA-600/8-80-030)

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----. 1992. Process Design Manual: Wastewater Treatment/Disposal for SmallCommunities. Cincinnati, Ohio. (Report No. EPA-625/R-92-005)

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